It popped from the exhaust 4 times during a 370 mile trip. Every time it was while cruising 80-85 MPH and happened just as I let up on the throttle, just one pop. Fuel economy & power seem normal, nothing else happening, plugs and all O2 sensors have 5-10k miles on them, throttle body and MAF cleaned at the same time. Current miles are 106K and I've had it since 70K. I've done the same drive several times and never experienced this. Only fault is for low cat efficiency which it's had for many years. Emissions tests are always clean, I just clear it before going to test.

 

Is this the first time you've done the same drive since changing the plugs and O2 sensors? You're not the guy that opted to put E3 spark plugs in, are you?

-Rod

 

I've done this drive at least once since the plugs & O2s, probably twice. And I generally drive about the same way when traffic allows.

I used Motorcraft plugs and Bosch O2s. The previous plugs were Champion platinum and I had a few issues with those so I swapped to the Motorcrafts.

 

If your scan tool has the ability to check for pending codes, I'd check that. See if maybe there is a pending code for a sensor that is providing odd or intermittent readings, such as the MAF sensor, TPS sensor, or maybe the Camshaft Position Sensor.

If this is truly a backfire, then something is causing at least one of the cylinder banks to run rich. Monitoring the fuel trims while driving might give a good indication of whether it is both banks or just one. You would also want to monitor the engine coolant temperature via the scan tool (not the gauge in the instrument cluster) to see if it seems reasonable along with the Intake Air Temperature sensor. If your scan tool has the ability to plot sensor data during datastream, then plot the Throttle Position Sensor to see if it tracks linearly when you let off the throttle. If both banks are tending rich, one of these sensors could be causing the engine to think either the temperature is different than it really is or something is telling the system to increase the injector pulse width to account for an incorrect amount of air or throttle input.

-Rod

 

No pending codes.

A backfire can be from a rich condition but can also be from a lean, misfire, or a bunch of other things. I hoped someone had some inside info on something with this vehicle that might be a common problem to cause this.

On my way back home from this trip it only did it once and it was milder than the previous events. Still a bit troubling since obviously something wasn't/isn't right.